A genetic bottleneck in the 'evolution under domestication' of upland cotton Gossypium hirsutum L. examined using DNA fingerprinting

Reliable information about the evolutionary and genetic relationships of va rious germplasm resources is essential to the establishment of rational str ategies for crop improvement. We used AFLPs to study the genetic relationsh ips of 43 cultivars of Gossypium hirsutum representative of the genomic com position of modern 'Upland' cotton. The study also included representatives of the related tetraploid species Gossypium barbadense, as well as the dip loid species Gossypium raimondii, Gossypium incanum, Gossypium herbaceum an d Gossypium arboreum. We tested 20 primer combinations that resulted in a t otal of 3,178 fragments. At the species level, and above, genetic similarit ies based on AFLPs were in agreement with the known taxonomic relationships . Similarity indices ranged from 0.25 to 0.99. Representatives of the G. hi rsutum germplasm resources utilized in North America, including secondary a ccessions collected by breeders in Central America ('Acala', 'Tuxtla', 'Kek chi') and the southwestern US (Hopi Moencopi'), formed a single cluster wit h exceedingly limited genetic diversity (with many pairwise similarity indi ces >0.96) We concluded that these accessions were derived from the same ge netic pool. The early maturing or 'latifolium' or 'Mexican Highlands' culti gens from which these cultivars were derived appear to have had extremely l imited genetic diversity, perhaps as a result of a severe genetic bottlenec k resulting, from the selection pressures of domestication. Outside of the major G. hirsutum cluster, well-supported phylogenies were inferred. Inside this cluster, phylogenies were obscured by limited diversity, reticulation and lineage sorting. The implications of these findings for cotton improve ment are discussed.